Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

Even though standard electrode potentials are determined for solutions in which the ion concentration is $1.0\,\text{mol dm}^{-3}$, batteries are usually run with solutions that are more concentrated. This question is about the electrode reactions occurring in the hydrogen-oxygen fuel cell and the lead-acid car battery.
(a(i))[1]

Using the Data Booklet, calculate $E_{\text{cell}}$ for this reaction.

(a(ii))[1]

Construct the overall reaction equation.

(a(iii))[2]

Using one of the phrases more positive, more negative or no change, deduce how increasing $[\text{OH}^- (aq)]$ affects the electrode potential of the left hand electrode and the right hand electrode.

(a(iv))[1]

Hence deduce whether the overall $E_{\text{cell}}$ will increase, decrease or stay the same when $[\text{OH}^- (aq)]$ increases. Explain your answer.

(a(v))[1]

Suggest one further reason for using a high $[\text{NaOH} (aq)]$ in the fuel cell.

(b(i))[1]

Using the Data Booklet, calculate $E_{\text{cell}}$ for this reaction.

(b(ii))[1]

Construct the equation for the overall reaction.

(b(iii))[1]

Construct the overall cell reaction equation in the presence of $\text{H}_2\text{SO}_4 (aq)$.

(b(iv))[2]

Considering how a decrease in $[\text{Pb}^{2+} (aq)]$ changes the cathode and anode potentials, deduce the effect of $\text{H}_2\text{SO}_4 (aq)$ in the electrolyte on the overall $E_{\text{cell}}$. State whether the $E_{\text{cell}}$ will increase, decrease or stay the same. Explain your answer.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Therefore, $E^\circ = 0.40 - (-0.83) = 1.23\,V$” …

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